Eyelid opening-extent detection apparatuses have been conventionally known. Japanese Patent No. 3143819 discloses therein an eyelid opening-extent detection apparatus, which detects a boundary point of an upper eyelid and an eyeball based upon a local maximal value point which has an edge value being a local maximal value or detects a boundary point of a lower eyelid and the eyeball based upon a local minimal value point which has an edge value being a local minimal value. Each boundary point is detected in a one-dimensional edge image representing a magnitude of grayscale change in a grayscale image. Specifically, the eyelid opening-extent detection apparatus searches edge local peak value points located most outward and determines the edge local peak value points searched as the boundary point of the upper eyelid and the eyeball and the boundary point of the lower eyelid and the eyeball, respectively.
However, the above described apparatus determines the edge local peak value points on the one-dimensional edge image, each of which has an edge value reaching maximum (upper eyelid) or minimum (lower eyelid), as the boundary points. In a case where an eyelid of an individual such as a driver is colored, such as where the eyelid is applied with eye shadow, a point distant from a boundary between the eyelid and an eyeball is erroneously detected as a boundary point. This may cause an erroneous detection of a boundary point.
A need thus exists for an eyelid detection apparatus and a program therefor, which are not susceptible to the drawback mentioned above.